Clarkson was forced to apologise and the regulator launched an investigation after his remark, made on The One Show, sparked around 31,700 complaints and led to condemnation from union leaders and politicians, with Prime Minister David Cameron branding the TV star's statement ''silly''.

On November 30, on the evening of Britain's biggest public sector strikes for 30 years, Clarkson said that he would take the striking workers outside and ''execute them in front of their families''.

Ofcom said that the comments, while ''potentially offensive'', were justified by the context.

Hosts Matt Baker and Alex Jones introduced Clarkson on The One Show by alluding to his provocative and outspoken nature, the watchdog said.

It added that viewers of the BBC1 show would have expected Clarkson to make ''potentially controversial or offensive statements'' because of his ''well-established public persona and that it would have been clear ''that his comments were not an expression of seriously held beliefs''.

Some viewers, less familiar with Clarkson's style, may have considered the comments offensive but the programme ended with an apology, Ofcom said.

The comments ''were not made seriously and were not at all likely to encourage members of the public...to act on them in any way'', it added.

Ofcom added that despite reports that Clarkson's comments were pre-approved by the BBC, he had in fact been advised by One Show producers not to air the sort of remark that he went on to make.

Last year, the BBC apologised about an item on BBC2's Top Gear which led to the Mexican ambassador complaining about the ''outrageous, vulgar and inexcusable insults'' made about Mexicans by Clarkson and co-hosts James May and Richard Hammond.

The BBC's editorial complaints unit upheld criticisms of the show and ruled that it reinforced stereotypes.

In February 2009, Clarkson famously called then-prime minister Gordon Brown a ''one-eyed Scottish idiot'' and in November the previous year, the BBC received almost 2,000 complaints when he joked about lorry drivers murdering prostitutes.